JP5787069B2 - Multi-wavelength semiconductor laser device - Google Patents

Description

  The present technology relates to a multi-wavelength semiconductor laser device having a monolithic structure, and more particularly to a multi-wavelength semiconductor laser device having an improved reflective film on the high reflectance side.

  In recent years, in the field of semiconductor laser elements (LD), multi-wavelength laser elements in which a plurality of light emitting portions having different emission wavelengths are monolithically formed on the same substrate have been actively developed. This multi-wavelength laser element is used, for example, as a light source of an optical disc apparatus.

  In such an optical disc apparatus, a laser beam of 790 nm band is used for reproducing a CD (Compact Disk), and a CD-R (CD Recordable), a CD-RW (CD Rewritable), or an MD (Mini Disk) can be recorded. It is used for recording / reproducing of an optical disc. A laser beam of 650 nm band is used for recording / reproduction of DVD (Digital Versatile Disk). By mounting a multi-wavelength laser element on an optical disk device, recording or reproduction can be performed for any of a plurality of existing types of optical disks. By increasing the number of wavelengths in this way, it is possible to further expand the applications.

  In a multi-wavelength laser element having a monolithic structure, generally, similarly to a single wavelength laser element, a low reflection film adapted to the wavelength of each laser beam is collectively formed on the entire front end face on the front end face of the laser element. High reflection films adapted to the wavelengths of the respective laser beams are collectively formed on the entire rear end surface on the rear end surface. At this time, in order to obtain a high reflectance, the high reflection film generally has a multilayer structure in which low refractive index layers and high refractive index layers are alternately laminated. It is comprised by the combination of the material from which the refractive index difference with a layer becomes large (refer patent document 1, 2).

  Usually, in a multi-wavelength laser element used for reproducing an optical disk, in order to adjust the light output emitted from the front end face, the light emitted from the rear end face is converted into a current by a photodiode and monitored. This monitor current largely depends on the reflectance of the rear end face. On the other hand, since the wavelength of the laser element varies with a change in temperature, the larger the amount of change of the reflectance on the rear end face with respect to the wavelength, the larger the change in the monitor current with respect to the temperature change of the element. .

Therefore, conventionally, in order to minimize the fluctuation amount of the reflectance of the high reflection film with respect to the wavelength change, as a material of the high reflection film, there is a material in which the refractive index difference between the low refractive index layer and the high refractive index layer is large. Has been used. For example, Al ₂ O ₃ (refractive index 1.64) is used as the material for the low refractive index layer, and Si (refractive index 3.3) is used as the material for the high refractive index layer.

JP 2008-16799 A JP 2010-171182 A

However, in a material having a refractive index exceeding 3.0, such as Si, light absorption at an oscillation wavelength of 650 nm is large, and film damage occurs. Therefore, there has been a problem that end face deterioration such as COD and ESD is likely to occur. Therefore, it is conceivable to use Ta ₂ O ₅ (refractive index of 2.1) with little light absorption instead of Si. However, in such a case, the difference in refractive index between the high refractive index layer and the low refractive index layer does not become as great as when Si is used for the high refractive index layer, so The fluctuation amount becomes large. As a result, there has been a problem that the monitor current fluctuates with the temperature change of the laser element.

  The present technology has been made in view of such problems, and its purpose is to reduce the variation in reflectance with respect to wavelength changes while suppressing the occurrence of end face deterioration, and to monitor the temperature change of the monitor current in each wavelength device. An object of the present invention is to provide a multi-wavelength semiconductor laser element that can be suppressed.

The first multi-wavelength semiconductor laser device according to the present technology is formed in a lump on each of the first element portion and the second element portion monolithically formed on the substrate and the rear end faces of the first element portion and the second element portion. And a rear end face film. The first element unit is a light emitting element unit having an oscillation wavelength of λ ₁ , and the second element unit is a light emitting element unit having an oscillation wavelength of λ ₂ (λ ₁ <λ ₂ ). The rear end face film is composed of N sets (N ≧ 2) of layers each including a combination of a low refractive index layer having a refractive index n _{1 and} a high refractive index layer having a refractive index n ₃ (n ₁ <n ₃ ). And an intermediate refractive index layer having a refractive index of n ₂ (n ₁ <n ₂ <n ₃ ) in that order from the rear end face side. The rear end face film is composed of a film different from the Si film. The optical thickness of the low refractive index layer, the high refractive index layer and the intermediate refractive index layer, a wavelength of between lambda ₁ and lambda ₂ when a lambda _3, and has a lambda _3/4.

In the first multiwavelength semiconductor laser device according to the present technology, the refractive index of the low refractive index layer and the refractive index of the high refractive index layer are formed on the surface of the layer in which the low refractive index layer and the high refractive index layer are alternately laminated on the rear end face. An intermediate refractive index layer having a refractive index between the indices is formed. Furthermore, these optical film thickness has a lambda _3/4. Thereby, the relationship of the reflectance with respect to the wavelength of the rear end face film in the wavelength band including λ ₁ and λ ₂ can be further flattened.

In the first multiwavelength semiconductor laser device according to the present technology, the refractive index n ₁ is a value of 1.4 or more and less than 1.5, and the refractive index n ₂ is a value of 1.5 or more and 1.7 or less. And the refractive index n ₃ is required to be 2.0 or more and 2.5 or less. For example, the material for the low refractive index layer includes SiO _{2 and the} like. Examples of the material for the high refractive index layer include Ta ₂ O ₅ , TiO ₂ , ZnO, HfO ₂ , CeO _{2, and} Nb ₂ O. Examples of the material for the intermediate refractive index layer include Al ₂ O _{3 and} MgO.

In the first multiwavelength semiconductor laser device according to the present technology, the low refractive index layer is a layer in which the SiO ₂ layer and the Al ₂ O ₃ layer or the MgO layer are combined, and the optical of the combined layer the film thickness may be made λ _3/4. In the first multiwavelength semiconductor laser device of the present technology, the low refractive index layer includes an Al ₂ O ₃ layer or an MgO layer, a Ta ₂ O ₅ layer, a TiO ₂ layer, a ZnO layer, an HfO ₂ layer, and a CeO ₂ layer. It has a layer in which a layer or Nb ₂ O layer was combined, and the optical thickness of the summed layers may be made λ _3/4.

The second multi-wavelength semiconductor laser element according to the present technology is formed in a lump on each of the first element part and the second element part monolithically formed on the substrate and the rear end surfaces of the first element part and the second element part. And a rear end face film. The first element unit is a light emitting element unit having an oscillation wavelength of λ ₁ , and the second element unit is a light emitting element unit having an oscillation wavelength of λ ₂ (λ ₁ <λ ₂ ). The rear end face film is composed of N pairs (N ≧ 2) in which the combination of the first low refractive index layer having a refractive index n ₁ and the high refractive index layer having a refractive index n ₃ (n ₁ <n ₃ ) is one set. ) A laminated layer and a second low refractive index layer having a refractive index n ₁ are included in order from the rear end face side. The rear end face film is composed of a film different from the Si film. Optical film thickness of the first low refractive index layer, the high refractive index layer and the second low refractive index layer, a wavelength of between lambda ₁ and lambda ₂ when a lambda _3, and has a lambda _3/4.

In the second multiwavelength semiconductor laser device according to the present technology, the same refractive index as the refractive index of the first low refractive index layer is formed on the surface of the layer in which the first low refractive index layer and the high refractive index layer are alternately stacked on the rear end face. A second low-refractive index layer is formed. Furthermore, these optical film thickness has a lambda _3/4. Thereby, the relationship of the reflectance with respect to the wavelength of the rear end face film in the wavelength band including λ ₁ and λ ₂ can be further flattened.

According to the first and second multiwavelength semiconductor laser elements according to the present technology, the reflectance of the rear end face film in the wavelength band including λ ₁ and λ ₂ is more flat with respect to the wavelength. It is possible to reduce the reflectance variation with respect to the wavelength variation, and to suppress the temperature change of the monitor current for monitoring the emitted light from the rear end face. Further, in the present technology, since the rear end face film does not include the Si film, the end face deterioration due to the Si film does not occur. From the above, in the present technology, it is possible to suppress the monitor current change accompanying the temperature change of the element while suppressing the occurrence of the end face deterioration.

It is the upper side figure and sectional drawing showing an example of the composition of the two-wavelength semiconductor laser device concerning one embodiment by this art. It is a figure showing an example of an internal structure of the rear end surface film | membrane of FIG. It is a figure showing an example of the reflectance distribution of the rear end surface side of the laser element provided with the rear end surface film which concerns on a comparative example. It is a figure showing the other example of the reflectance distribution of the rear end surface side of the laser element provided with the rear end surface film which concerns on a comparative example. It is a figure showing an example of the composition of the back end face film concerning a comparative example. FIG. 6 is a diagram illustrating an example of a reflectance distribution on a rear end surface side of a laser element including the rear end surface film of FIG. 5. It is a figure showing an example of the reflectance distribution of the rear end surface side of the laser element provided with the rear end surface film of FIG. FIG. 10 is a top view illustrating a modification of the configuration of the two-wavelength semiconductor laser device in FIG. 1. It is a figure showing an example of a structure of the rear-end surface film | membrane of FIG. It is a figure showing the other example of a structure of the rear-end surface film | membrane of FIG. FIG. 10 is a top view illustrating another modification of the configuration of the two-wavelength semiconductor laser device in FIG. 1. It is a figure showing an example of a structure of the rear end surface film | membrane of FIG.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the invention will be described in detail with reference to the drawings. The description will be given in the following order.

1. Embodiment
1. An example in which the intermediate refractive index layer is provided on the outermost surface side of the rear end face film. Modified example
Example of low refractive index layer consisting of multiple layers
Example in which the intermediate refractive index layer is also provided on the rear end face side of the rear end face film

<1. Embodiment>
FIG. 1A shows a planar configuration of a two-wavelength semiconductor laser device 1 according to an embodiment of the present technology. FIG. 1B shows a cross-sectional configuration of the two-wavelength semiconductor laser device 1 of FIG. 1A and 1B are schematic representations, and are different from actual dimensions and shapes. The two-wavelength semiconductor laser element 1 corresponds to a specific example of “multi-wavelength semiconductor laser element” in the claims.

  The two-wavelength semiconductor laser device 1 includes a first element portion 20A and a second element portion 20B that are monolithically formed on a substrate 10.

(First element portion 20A)
The first element unit 20A is a semiconductor laser element having an oscillation wavelength of λ _A. Specifically, λ _A is a wavelength in the 650 nm band. The first element portion 20A is made of an aluminum / gallium / indium / phosphorus (AlGaInP) III-V compound semiconductor. The aluminum, gallium, indium, and phosphorus group III-V compound semiconductor here means at least aluminum (Al), gallium (Ga), and indium (In) among the 3B group elements in the short period type periodic table, and short. It refers to those containing at least phosphorus (P) among the group 5B elements in the periodic periodic table.

  The first element portion 20A is obtained by growing a semiconductor layer 21A on the substrate 10. The semiconductor layer 21A includes an n-type cladding layer, an active layer 22A, a p-type cladding layer, and a p-side contact layer. Note that layers other than the active layer 22A are not particularly shown.

Specifically, the substrate 10 is made of, for example, n-type GaAs. The n-type cladding layer is made of, for example, n-type AlGaInP. The active layer 22A has, for example, a multiple quantum well structure in which well layers and barrier layers are alternately stacked. The well layer and the barrier layer are made of, for example, Al _x Ga _y In _1-xy P (where x ≧ 0 and y ≧ 0) having different composition ratios. The p-type cladding layer is made of, for example, p-type AlGaInP. The p-side contact layer is made of, for example, p-type GaAs. A part of the p-type cladding layer and the p-side contact layer form a stripe-shaped ridge portion 23A extending in the direction of the resonator, so that current confinement is achieved. In the active layer 22A, a region corresponding to the region immediately below the ridge 23A is a light emitting region 24A.

An insulating layer 25 is provided on the continuous surface from the side surface of the ridge portion 23A to the surface of the p-type cladding layer. The insulating layer 25 is made of, for example, an insulating material such as SiO ₂ , ZrOx, or SiN, and electrically insulates the semiconductor layer 21A of the first element unit 20A from the semiconductor layer 21B (described later) of the second element unit 20B. In addition, current can flow into the active layer 22A only from the upper surfaces of the ridge portion 23A and the ridge portion 23B (described later). Therefore, the insulating layer 25 has an element isolation function and a current confinement function.

  An upper electrode 26A is provided on a continuous surface from the upper surface of the ridge portion 23A (the surface of the p-side contact layer) to the surface of the insulating layer 25, and is electrically connected to the p-side contact layer. On the other hand, a lower electrode 27 is provided on the back surface of the substrate 10 and is electrically connected to the substrate 10.

  The upper electrode 26A is electrically connected to a wiring (not shown), and is connected to a positive power source (not shown) via the wiring. The lower electrode 27 is electrically connected to a wiring (not shown), and is connected to a negative power source (not shown) via the wiring. Here, the upper electrode 26A and the lower electrode 27 have a multilayer structure in which, for example, titanium (Ti), platinum (Pt), and gold (Au) are laminated in this order. The wiring connected to the upper electrode 26A and the lower electrode 27 is made of, for example, Au.

(Second element portion 20B)
The second element unit 20B is a semiconductor laser element having an oscillation wavelength of λ _B (λ _A <λ _B ). Specifically, λ _B is a wavelength in the 790 nm band. The second element portion 20B is made of a gallium arsenide (GaAs) III-V group compound semiconductor. The gallium-arsenic III-V group compound semiconductor here is at least gallium (Ga) of 3B group elements in the short period type periodic table, and at least arsenic of 5B group elements in the short period type periodic table. As).

  The second element portion 20B is obtained by growing a semiconductor layer 21B on the substrate 10 like the first light emitting element 20A. The semiconductor layer 21B includes an n-type cladding layer, an active layer 22B, a p-type cladding layer, and a p-side contact layer. The layers other than the active layer 22B are not particularly shown.

  Specifically, the n-type cladding layer is made of, for example, n-type AlGaAs. The active layer 22B has, for example, a multiple quantum well structure in which well layers and barrier layers are alternately stacked. Each of the well layer and the barrier layer is made of, for example, AlxGa1-xAs (where x ≧ 0) having different compositions. The p-type cladding layer is made of, for example, p-type AlGaAs. The p-side contact layer is made of, for example, p-type GaAs. A part of the p-type cladding layer and the p-side contact layer have a striped ridge portion 23B extending in the direction of the resonator, so that current confinement is achieved. In the active layer 22B, a region corresponding to the ridge portion 23B is a light emitting region 24B.

  The insulating layer 25 described above is provided on a continuous surface (hereinafter referred to as surface B) from the side surface of the ridge portion 23B to the surface of the p-type cladding layer.

  An upper electrode 26B is provided on a continuous surface from the upper surface of the ridge portion 23B (the surface of the p-side contact layer) to the surface of the insulating layer 25, and is electrically connected to the p-side contact layer. On the other hand, the lower electrode 27 described above is provided on the back surface of the substrate 10 and is electrically connected to the substrate 10.

  The upper electrode 26B is connected to a positive power source (not shown) via a wiring (not shown). Here, the upper electrode 26B is configured by, for example, laminating Ti, Pt, and Au in this order. The wiring layer 28B is made of, for example, Au.

(Front end face film, rear end face film)
As shown in FIG. 1A, the two-wavelength semiconductor laser device 1 further has a surface (front end surface) perpendicular to the extending direction (resonator direction) of the first element portion 20A and the second element portion 20B. A pair of front end face film 30 and rear end face film 40 are provided on S1 and rear end face S2).

  The front end face film 30 is collectively formed on the entire front end face S1. The front end face film 30 is configured such that the reflectance of the front end face S1 of the two-wavelength semiconductor laser element 1 is, for example, 35% or less in the wavelength band of the light emitted from the first element part 20A and the second element part 20B. Yes. For example, the front end face film 30 is configured by alternately laminating low refractive index layers and high refractive index layers on the front end face S1.

  On the other hand, the rear end face film 40 is formed collectively on the entire rear end face S2. The rear end face film 40 has a reflectivity of the rear end face S2 of the two-wavelength semiconductor laser device 1 of, for example, not less than 50% and not more than 85% in the wavelength band of light emitted from the first element portion 20A and the second element portion 20B. It is configured.

  The rear end face film 40 has a base layer 41 in contact with the rear end face S2. The rear end face film 40 further includes a laminated film formed by laminating a plurality of layers each including a low refractive index layer 42 and a high refractive index layer 43 on the base layer 41, and an intermediate refractive index layer 44. In order from the rear end face S2 side. The rear end face film 40 does not include a silicon (Si) film and is formed of a film different from the Si film. The underlayer 41 can be omitted as necessary. When the base layer 41 is omitted, the low refractive index layer 42 closest to the rear end surface S2 is in contact with the rear end surface S2. The rear end face film 40 may have some layer such as a protective film on the intermediate refractive index layer 44.

The low refractive index layer 42 corresponds to a specific example of “low refractive index layer” in the claims. The high refractive index layer 43 corresponds to a specific example of “high refractive index layer” in the claims. The intermediate refractive index layer 44 corresponds to a specific example of “intermediate refractive index layer” in the claims.

The underlayer 41 is made of a highly stable material that does not adversely affect the rear end surface S2, and is made of, for example, Al ₂ O ₃ . The refractive index of the base layer 41 is, for example, a value between the refractive index of the low refractive index layer 42 and the refractive index of the high refractive index layer 43. The optical film thickness of the underlayer 41 is a thickness adjusted so that the total optical film thickness of the underlayer 41 and the low refractive index layer 42 in contact with the underlayer 41 is λ _C / 4. Here, λ _C is a wavelength larger than λ _A and smaller than λ _B , for example, (λ _A + λ _B ) / 2.

The refractive index and the optical film thickness of the low refractive index layer 42, the high refractive index layer 43, and the intermediate refractive index layer 44 are as follows.
(When the base layer 41 is omitted)
Refractive index Optical thickness Low refractive index layer 42: n _A λ _C / 4
High refractive index layer 43: n _B λ _C / 4
Intermediate refractive index layer 44: n _C λ _C / 4
λ _A <λ _C <λ _B
n _A <n _C <n _B
(When the base layer 41 is provided)
Refractive index Optical film thickness Low refractive index layer 42 in contact with base layer 41: n _A (λ _C / 4) − (optical film thickness of base layer 41)
Low refractive index layer 42 not in contact with underlying layer 41: n _A λ _C / 4
High refractive index layer 43: n _B λ _C / 4
Intermediate refractive index layer 44: n _C λ _C / 4

Here, the refractive index n _A is a value of 1.4 or more and less than 1.5. The refractive index n _B is a value of 2.0 or more and 2.5 or less. The refractive index n _C is a value of 1.5 or more and 1.7 or less. The low refractive index layer 42 is a SiO ₂ film (refractive index 1.45). The high refractive index layer 43 is a Ta ₂ O ₅ film (refractive index 2.1), TiO ₂ film, ZnO film, HfO ₂ film, CeO ₂ film or Nb ₂ O film. The intermediate refractive index layer 44 is an Al ₂ O ₃ film (refractive index 1.64) or an MgO film.

FIG. 2 shows an example of the configuration of the rear end face film 40. Although two configurations are illustrated in FIG. 2, each example illustrates a case where three layers each including the low refractive index layer 42 and the high refractive index layer 43 are stacked. Yes. In the upper example of FIG. 2, the base layer 41 is made of Al ₂ O ₃ , the low refractive index layer 42 is made of an SiO ₂ film, the high refractive index layer 43 is made of a Ta ₂ O ₅ film, and intermediate refraction. The rate layer 44 is composed of an Al ₂ O ₃ film. On the other hand, the lower example in FIG. 2 is obtained by omitting the base layer 41 in the upper example in FIG. In the lower example of FIG. 2, the low refractive index layer 42 is in direct contact with the rear end surface S2.

[Production method]
The two-wavelength semiconductor laser device 1 having such a configuration can be manufactured, for example, as follows.

  First, the laser structure of the first element unit 20A is manufactured. For this purpose, the semiconductor layer 21A on the substrate 10 is formed by, for example, the MOCVD method. At this time, for example, trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMIn), and phosphine (PH3) are used as the raw material for the AlGaInP-based semiconductor. For example, hydrogen selenide ( H2Se) is used, and dimethylzinc (DMZn), for example, is used as the acceptor impurity material.

  Specifically, first, an n-side contact layer, an n-type cladding layer, an active layer 22A, a p-type cladding layer, and a p-type contact layer are stacked in this order on the substrate 10 to form the semiconductor layer 21A. Subsequently, the p-side contact layer and the p-type cladding layer are patterned, for example, by a dry etching method so as to form a thin band-like convex portion, thereby forming a ridge portion 23A.

  Next, the laser structure of the second element unit 20B is manufactured. For this purpose, the semiconductor layer 21B on the substrate 10 is formed by, for example, the MOCVD method. At this time, for example, TMA, TMG, TMIn, and arsine (AsH3) are used as a GaAs-based semiconductor material, H2Se is used as a donor impurity material, and DMZn is used as an acceptor impurity material, for example.

  Specifically, first, an n-side contact layer, an n-type cladding layer, an active layer 22B, a p-type cladding layer, and a p-type contact layer are stacked in this order on the substrate 10 to form the semiconductor layer 21B. Subsequently, the p-side contact layer and the p-type cladding layer are patterned, for example, by a dry etching method so as to form a thin band-like convex portion, thereby forming a ridge portion 23B. Thereby, as shown in FIG. 1B, the laser structure of the first element unit 20A and the laser structure of the second element unit 20B are arranged on the substrate 10.

  Next, after an insulating material such as SiN is formed on the surface including the upper surfaces of the ridge portions 23A and 23B by vapor deposition or sputtering, regions of the insulating material corresponding to the upper surfaces of the ridge portions 23A and 23B are removed by etching. Thereby, the insulating layer 25 is formed.

  Next, as shown in FIGS. 1A and 1B, the upper electrode 26A is formed on the continuous surface from the surface of the p-side contact layer to the surface of the insulating layer 25 of the ridge portion 23A. Further, the upper electrode 26B is formed on the continuous surface from the surface of the p-side contact layer of the ridge portion 23B to the surface of the insulating layer 25. Further, the lower electrode 27 is formed on the back surface of the substrate 10.

  Next, the front end face S1 and the rear end face S2 are cleaved along a plane perpendicular to the extending direction of the ridge portions 23A and 23B, and then the front end face film 30 is formed on the front end face S1 and the rear end face S2 is rear end. The face film 40 is formed at once. In this way, the two-wavelength semiconductor laser device 1 of the present embodiment is manufactured.

[Action, effect]
Next, the operation and effect of the two-wavelength semiconductor laser device 1 of the present embodiment will be described.

  In the two-wavelength semiconductor laser device 1 of the present embodiment, when a predetermined voltage is applied between the upper electrodes 26A and 26B and the lower electrode 27, current is injected into the active layers 22A and 22B, and electron-holes are injected. Luminescence occurs due to recombination. The light emitted from each of the active layers 22A and 22B is reflected by the front end face film 30 and the rear end face film 40 to cause laser oscillation, and laser light having a wavelength of 650 nm from the first element portion 20A side of the front end face film 30 is converted into the front end face film. 30, laser light having a wavelength of 790 nm is emitted to the outside from the second element portion 20B side. In this way, laser beams having different wavelengths are emitted from the first element unit 20A and the second element unit 20B.

  By the way, in the multi-wavelength laser element used for reproducing the optical disk, in order to adjust the light output emitted from the front end face, the light emitted from the rear end face is converted into a current by a photodiode and monitored. It largely depends on the reflectance of the rear end face. On the other hand, since the wavelength of the laser element varies with a change in temperature, the larger the amount of change of the reflectance on the rear end face with respect to the wavelength, the larger the change in the monitor current with respect to the temperature change of the element. .

Therefore, conventionally, in order to minimize the fluctuation amount of the reflectance of the high reflection film with respect to the wavelength change, as a material of the high reflection film, there is a material in which the refractive index difference between the low refractive index layer and the high refractive index layer is large. Has been used. For example, Al ₂ O ₃ (refractive index 1.64) is used as the material for the low refractive index layer, and Si (refractive index 3.3) is used as the material for the high refractive index layer. Note that the reflectivity of the highly reflective film at this time has a profile as shown in FIG. 3, for example.

However, in a material having a refractive index exceeding 3.0, such as Si, light absorption at an oscillation wavelength of 650 nm is large, and film damage occurs. Therefore, end face deterioration such as COD and ESD is likely to occur. Therefore, it is conceivable to use Ta ₂ O ₅ (refractive index 2.1) with little light absorption instead of Si, and use SiO ₂ instead of Al ₂ O _{3 in} order to increase the refractive index difference. However, in this case, for example, as shown in FIG. 4, the amount of variation of the reflectance of the highly reflective film with respect to the wavelength variation becomes larger than the amount of variation in FIG. There was a problem that the fluctuation of the monitor current accompanying the increase.

In Patent Documents 1 and 2, as shown in FIG. 5, Al ₂ O ₃ is formed in the first layer, Ta ₂ O ₅ is formed in the _second layer, SiO ₂ is formed in the third layer, and Ta ₂ is formed in the fourth layer. the ₂ O _5, the SiO ₂ in the fifth layer, the Ta ₂ O ₅ to 6 th layer, the SiO ₂ in the seventh layer, it has been proposed to use Ta ₂ O ₅ in the eighth layer. In the example of FIG. 5, the optical film thickness from the first layer to the seventh layer is λ / 4, and only the optical film thickness of the eighth layer is λ / 2. However, in this case, for example, as shown in FIG. 6, the amount of fluctuation of the reflectance of the highly reflective film with respect to the wavelength change is still large, and the fluctuation of the monitor current accompanying the temperature change of the laser element becomes large. There was a problem.

On the other hand, in the present embodiment, the refractive index n _A of the low refractive index layer 42 and the high refractive index layer 43 are formed on the surface of the layer in which the low refractive index layers 42 and the high refractive index layers 43 are alternately stacked on the rear end surface S2. An intermediate refractive index layer 44 having a refractive index n _C between these refractive indexes n _B is formed. Further, when the base layer 41 is omitted, these optical film thicknesses are λ _C / 4. When the base layer 41 is provided, the optical film thickness of each of the low refractive index layer 42, the high refractive index layer 43, and the intermediate refractive index layer 44 that is not in contact with the base layer 41 is λ _C. / 4, and the optical film thickness of the low refractive index layer 42 in contact with the base layer 41 is (λ _C / 4) − (the optical film thickness of the base layer 41). Thereby, for example, as shown in FIG. 7, the change in the wavelength of the reflectance of the rear end face film 40 in the wavelength band including the oscillation wavelengths λ _A and λ _B is made larger than the change in the wavelength of the reflectivity in FIGS. It can be flattened. As a result, it is possible to reduce the fluctuation of the monitor current accompanying the temperature change of the laser element. Furthermore, in the present embodiment, the rear end face film 40 does not include a Si film, and therefore, end face deterioration due to light absorption of the Si film does not occur. From the above, in the present embodiment, it is possible to suppress a change in the monitor current accompanying a temperature change of the element while suppressing the occurrence of end face deterioration.

  Further, in the present embodiment, the rear end face film 40 has a single configuration formed in a lump on the rear end face S2 as described above, and the material or film depending on the portion from which the laser light is emitted. It does not have a plurality of structures in which the thickness, layer structure, etc. are adjusted. As a result, the rear end face film 40 can be formed with a small number of process steps, so that the two-wavelength semiconductor laser device 1 can be manufactured at low cost.

<2. Modification>
(First modification)
In the above embodiment, the oscillation wavelength λ _A of the first element unit 20A is in the 650 nm band, and the oscillation wavelength λ _B of the second element unit 20B is in the 790 nm band. The oscillation wavelengths λ _A and λ _{B of the} two-element unit 20B may be different from the above. However, the oscillation wavelengths λ _A and λ _B are adjusted by adjusting the optical film thickness λ _C / 4 of each layer included in the rear end face film 40, thereby adjusting the rear end face film 40 in the wavelength band including the oscillation wavelengths λ _A and λ _B. It is necessary that the reflectance is within a range where the reflectance can be flattened. Indeed, the applicant, the oscillation wavelength lambda _A, lambda if _B is sufficient that the 300nm or 900nm or less, to a uniform reflectivity of the rear end face film 40 at a wavelength band including an oscillation wavelength lambda _A, the lambda _B Confirm that you can.

In principle, even when the oscillation wavelengths λ _A and λ _B are larger than 900 nm, the reflectance of the rear end face film 40 in the wavelength band including λ _A and λ _B can be flattened. it can. Further, as the optical film thickness λ _C / 4 of each layer included in the rear end face film 40 increases, the width of the wavelength band in which the reflectivity of the rear end face film 40 becomes flat becomes wider. Accordingly, the wavelength difference between the oscillation wavelengths λ _A and λ _B can be increased as the optical film thickness λ _C / 4 of each layer included in the rear end face film 40 is increased.

(Second modification)
In the above embodiment, the low refractive index layer 42 is composed of a single layer, but may be composed of a plurality of layers. For example, as shown in FIG. 8, the low refractive index layer 42 includes a first refractive index layer 42A having a refractive index n _A and a second refractive index layer 42B having a refractive index n _C from the rear end face S2 side. It may be a laminated body formed by laminating. When the base layer 41 is omitted, the total optical film thickness of the first refractive index layer 42A and the second refractive index layer 42B is λ _C / 4. When the base layer 41 is omitted, the first refractive index layer 42A closest to the rear end surface S2 is in contact with the rear end surface S2. When the base layer 41 is provided, the total optical film thickness of the first refractive index layer 42A and the second refractive index layer 42B in the low refractive index layer 42 not in contact with the base layer 41 is λ _C In the low refractive index layer 42 in contact with the foundation layer 41, the total optical film thickness of the first refractive index layer 42A and the second refractive index layer 42B is (λ _C / 4) − (underlayer). 41). At this time, the first refractive index layer 42A is composed of an SiO ₂ film, and the second refractive index layer 42B is composed of an Al ₂ O ₃ film or an MgO film. For example, as illustrated in the upper and lower stages of FIG. 9, the first refractive index layer 42A may be composed of a SiO ₂ film, and the second refractive index layer 42B may be composed of an Al ₂ O ₃ film. Further, for example, as illustrated in the upper and lower stages of FIG. 10, the first refractive index layer 42A may be composed of an Al ₂ O ₃ film, and the second refractive index layer 42B may be composed of a Ta ₂ O ₅ film. Good.

Even in the case where the rear end face film 40 has such a configuration, the wavelength change of the reflectance of the rear end face film 40 in the wavelength band including the oscillation wavelengths λ _A and λ _B is changed as in the above embodiment. It can be flattened rather than the wavelength change of the reflectance in FIGS. As a result, it is possible to reduce the fluctuation of the monitor current accompanying the temperature change of the laser element. Further, in this modification as well, the rear end face film 40 does not include the Si film, so that end face deterioration due to light absorption of the Si film does not occur. From the above, also in this modification, it is possible to suppress the monitor current change accompanying the temperature change of the element while suppressing the occurrence of the end face deterioration.

(Third Modification)
In the above embodiment, for example, as shown in FIG. 11, an intermediate refractive index layer 45 may be provided instead of the low refractive index layer 42. In this case, the base layer 41 can be omitted as shown in FIG. In the following description, it is assumed that the base layer 41 is omitted and the intermediate refractive index layer 45 closest to the rear end surface S2 is in contact with the rear end surface S2.

In the present modification, the intermediate refractive index layer 45 corresponds to a specific example of “first low refractive index layer” in the claims. The high refractive index layer 43 corresponds to a specific example of “high refractive index layer” in the claims. The intermediate refractive index layer 44 corresponds to a specific example of “second low refractive index layer” in the claims.

The refractive index and optical film thickness of the intermediate refractive index layer 45, the high refractive index layer 43, and the intermediate refractive index layer 44 are as follows.
Refractive index Optical thickness Intermediate refractive index layer 45: n _D λ _C / 4
High refractive index layer 43: n _B λ _C / 4
Intermediate refractive index layer 44: n _C λ _C / 4
n _D = n _C <n _B

Here, the refractive indexes n _C and n _D are both the same and have a value of 1.5 or more and 1.7 or less. The refractive index n _B is a value of 2.0 or more and 2.5 or less. The intermediate refractive index layers 44 and 45 are both made of the same material, specifically, an Al ₂ O ₃ film or an MgO film. The high refractive index layer 43 is a Ta ₂ O ₅ film, a TiO ₂ film, a ZnO film, an HfO ₂ film, a CeO ₂ film, or an Nb ₂ O film.

FIG. 12 shows an example of the configuration of the rear end face film 40. FIG. 12 illustrates a case where three sets of layers each including the intermediate refractive index layer 45 and the high refractive index layer 43 are stacked. In the example of FIG. 12, the intermediate refractive index layer 45 is composed of a SiO ₂ film, and the high refractive index layer 43 is composed of a Ta ₂ O ₅ film.

Even in the case where the rear end face film 40 has such a configuration, the wavelength change of the reflectance of the rear end face film 40 in the wavelength band including the oscillation wavelengths λ _A and λ _B is changed as in the above embodiment. It can be flattened rather than the wavelength change of the reflectance in FIGS. As a result, it is possible to reduce the fluctuation of the monitor current accompanying the temperature change of the laser element. Further, in this modification as well, the rear end face film 40 does not include the Si film, so that end face deterioration due to light absorption of the Si film does not occur. From the above, also in this modification, it is possible to suppress the monitor current change accompanying the temperature change of the element while suppressing the occurrence of the end face deterioration.

  Although the present technology has been described with the embodiment and the modification, the present technology is not limited to the above-described embodiment and the like, and various modifications can be made.

  For example, in the above-described embodiments and modifications, p-type and n-type conductivity types may be opposite to those described above. In the above-described embodiment and modification, the case where the present technology is applied to a two-wavelength semiconductor laser element has been described, but it is naturally possible to apply the present technique to a semiconductor laser element having three or more wavelengths.

For example, this technique can take the following composition.
(1)
A first element part and a second element part monolithically formed on the substrate;
A rear end face film formed on the rear end face of each of the first element part and the second element part,
The first element portion is a light emitting element portion having an oscillation wavelength of λ ₁
The second element part is a light emitting element part having an oscillation wavelength of λ ₂ (λ ₁ <λ ₂ ),
The rear end face film is composed of N pairs (N ≧ 2) in which a combination of a low refractive index layer having a refractive index n _{1 and} a high refractive index layer having a refractive index n ₃ (n ₁ <n ₃ ) is one set. It includes a stacked layer and an intermediate refractive index layer having a refractive index of n ₂ (n ₁ <n ₂ <n ₃ ) in order from the rear end face side, and is composed of a film different from the Si film,
The low refractive index layer, the optical thickness of the high refractive index layer and the intermediate refractive index layer, a wavelength of between lambda ₁ and lambda ₂ when the λ _3, λ _3/4 and going on multiwavelength Semiconductor laser element.
(2)
The refractive index n ₁ is a value of 1.4 or more and less than 1.5,
The refractive index n ₂ is a value of 1.5 or more and 1.7 or less,
Multi-wavelength semiconductor laser device according to the refractive index n ₃ is 2.0 to 2.5 of the value (1).
(3)
The low refractive index layer is a SiO ₂ layer,
The high refractive index layer is a Ta ₂ O ₅ layer, a TiO ₂ layer, a ZnO layer, an HfO ₂ layer, a CeO ₂ layer or an Nb ₂ O film,
The multi-wavelength semiconductor laser device according to (2), wherein the intermediate refractive index layer is an Al ₂ O ₃ layer or an MgO layer.
(4)
The low refractive index layer is a laminate of an SiO ₂ layer and an Al ₂ O ₃ layer or an MgO layer,
The high refractive index layer is a Ta ₂ O ₅ layer, a TiO ₂ layer, a ZnO layer, an HfO ₂ layer, a CeO ₂ layer or an Nb ₂ O layer,
The multi-wavelength semiconductor laser device according to (2), wherein the intermediate refractive index layer is an Al ₂ O ₃ layer or an MgO layer.
(5)
The multi-wavelength semiconductor laser device according to any one of (1) to (4), wherein the low refractive index layer closest to the rear end surface is in contact with the rear end surface.
(6)
The rear end face film has a refractive index n ₄ (n ₁ <n ₄ <n ₃ ) and a refractive index n ₁ between the rear end face and the low refractive index layer closest to the rear end face. A second low refractive index layer and a second high refractive index layer having a refractive index of n ₃ in order from the rear end face side,
Optical film thickness of the second high refractive index layer is a lambda _3/4,
Optical film thickness of the second low refractive index layer, (lambda _3/4) - has a (optical film thickness of the underlying layer),
The optical thickness of the underlayer is to optical total thickness of the undercoat layer and the second low refractive index layer is (is 1) to a thickness which is adjusted so that the lambda _3/4 (4) The multiwavelength semiconductor laser device according to any one of the above.
(7)
A first element part and a second element part monolithically formed on the substrate;
A rear end face film formed on the rear end face of each of the first element part and the second element part,
The first element portion is a light emitting element portion having an oscillation wavelength of λ ₁
The second element part is a light emitting element part having an oscillation wavelength of λ ₂ (λ ₁ <λ ₂ ),
The rear end face film is composed of N sets (N ≧ N ≧) of a combination of a first low refractive index layer having a refractive index n _{1 and} a high refractive index layer having a refractive index n ₃ (n ₁ <n ₃ ). 2) It includes a laminated layer and a second low refractive index layer having a refractive index n ₁ in order from the rear end face side, and is composed of a film different from the Si film.
The first low refractive index layer, the optical thickness of the high refractive index layer and the second low refractive index layer, a wavelength of between lambda ₁ and lambda ₂ when a lambda _3, a lambda _3/4 A multi-wavelength semiconductor laser device.
(8)
The refractive index n ₁ is a value of 1.5 or more and 1.7 or less,
The refractive index n ₃ is a value of 2.0 or more and 2.5 or less,
The multiwavelength semiconductor laser device according to (7).
(9)
The first low refractive index layer and the second low refractive index layer are both Al ₂ O ₃ layers or MgO layers,
The multi-wavelength semiconductor laser device according to (8), wherein the high refractive index layer is a Ta ₂ O ₅ layer, a TiO ₂ layer, a ZnO layer, an HfO ₂ layer, a CeO ₂ layer, or an Nb ₂ O layer.
(10)
The multi-wavelength semiconductor laser device according to (7), wherein the first low refractive index layer closest to the rear end surface is in contact with the rear end surface.

  DESCRIPTION OF SYMBOLS 1 ... 2 wavelength semiconductor laser element, 10 ... Board | substrate, 20A ... 1st element part, 20B ... 2nd element part, 21A, 21B ... Semiconductor layer, 22A, 22B ... Active layer, 23A, 23B ... Ridge part, 24A, 24B ... light emitting region, 25 ... insulating layer, 26A, 26B ... upper electrode, 27 ... lower electrode, 30 ... front end face film, 40 ... rear end face film, 41 ... underlayer, 42 ... low refractive index layer, 43 ... high refractive index Layer, 44, 45 ... Intermediate refractive index layer, S1 ... Front end face, S2 ... Rear end face.

Claims (3)

A first element part and a second element part monolithically formed on the substrate;
A rear end face film formed on the rear end face of each of the first element part and the second element part,
The first element portion is a light emitting element portion having an oscillation wavelength of λ ₁
The second element part is a light emitting element part having an oscillation wavelength of λ ₂ (λ ₁ <λ ₂ ),
The rear end face film is composed of N pairs (N ≧ 2) in which a combination of a low refractive index layer having a refractive index n _{1 and} a high refractive index layer having a refractive index n ₃ (n ₁ <n ₃ ) is one set. It includes a stacked layer and an intermediate refractive index layer having a refractive index of n ₂ (n ₁ <n ₂ <n ₃ ) in order from the rear end face side, and is composed of a film different from the Si film,
The low refractive index layer, the optical thickness of the high refractive index layer and the intermediate refractive index layer, a wavelength of between lambda ₁ and lambda ₂ when a lambda _3, has a lambda _3/4,
The rear end face film has a refractive index n ₄ (n ₁ <n ₄ <n ₃ ) and a refractive index n ₁ between the rear end face and the low refractive index layer closest to the rear end face. A second low refractive index layer and a second high refractive index layer having a refractive index of n ₃ in order from the rear end face side,
Optical film thickness of the second high refractive index layer is a lambda _3/4,
Optical film thickness of the second low refractive index layer, (lambda _3/4) - has a (optical film thickness of the underlying layer),
The optical thickness of the underlayer is a multi-wavelength semiconductor laser device has a thickness that the optical thickness of the sum of the base layer and the second low refractive index layer is adjusted to be λ _3/4. The refractive index n ₁ is a value of 1.4 or more and less than 1.5,
The refractive index n ₂ is a value of 1.5 or more and 1.7 or less,
The multi-wavelength semiconductor laser device according to claim 1, wherein the refractive index n ₃ is a value of 2.0 or more and 2.5 or less. The low refractive index layer is a SiO ₂ layer,
The high refractive index layer is a Ta ₂ O ₅ layer, a TiO ₂ layer, a ZnO layer, an HfO ₂ layer, a CeO ₂ layer or an Nb ₂ O ₅ film,
The multiwavelength semiconductor laser device according to claim 2, wherein the intermediate refractive index layer is an Al ₂ O ₃ layer or an MgO layer.

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